1. Field of the Invention
The invention relates to an image pickup apparatus, and more particularly, relates to an image pickup apparatus having characteristic features with respect to a lens (group) that is disposed closest to the image plane.
2. Description of the Related Art
Lens barrels, in which the length thereof in the optical axis direction can be reduced (to enable a slimmer design) in a fully-retracted state (accommodated state), that are suitable for a portable optical apparatus such as a camera, etc., have been proposed by the inventors of the present invention in Japanese Patent No. 3,771,909 and Japanese Unexamined Patent Publication No. 2009-251063.
In an image pickup apparatus provided with the above-mentioned lens barrel, a focus lens group of a photographing optical system is disposed closest to the image plane (image pickup device/image sensor). In general, since the focus lens group is circular as seen in a front elevational view, an image shape (image circle) formed by the photographing optical system including the focus lens group is circular. Whereas, since a light-receiving surface (area) of the image sensor has an aspect ratio of 4:3, i.e., a rectangular shape, an optical region (area) which does not contribute to the formation of an object image in the light-receiving surface exists within the image circle. If the image formed by the photographing optical system has a size and shape capable of covering the light-receiving surface of the image sensor, the image need not necessarily be circular. In the related art, an image pickup apparatus is known in which the lens group that is provided closest to the image plane is formed into a rectangular shape in a front elevational view (when viewed in the optical axis direction), similar to the shape of the image sensor, by eliminating the optical region of the lens group which does not contribute to the formation of the object image on the rectangular light-receiving surface from the front elevational circular shape thereof. In this manner, the unnecessary optical region is eliminated from the circular lens, so that it is possible to achieve a small-sized (miniaturized) and light-weight image pickup apparatus.
On the other hand, it has been desirable for such image pickup apparatuses to be assembled in the state where the lens barrel (the entirety thereof or only the focus lens group) is rotated by 90 degrees about the optical axis relative to the image sensor in accordance with to the shape, the specification, etc., of the mounted optical apparatus. However, although the front elevation of the focus lens group is a rectangle corresponding to the aspect ratio of the rectangular light-receiving surface of the image sensor, since the contour of the image formed by the image pickup apparatus is also rectangular, if the focus lens group is rotated by 90 degrees about the optical axis, the contour of the image is also rotated by 90 degrees, so that a portion of the light-receiving surface of the image sensor in the longitudinal direction exceeds the contour of the image. Conventionally, in order to satisfy the desire to assemble the image pickup apparatus by rotating the lens barrel (focus lens group) relative to the image pickup device, a focus lens group having a circular shape in a front elevational view must be used, so that the desire for a small-sized and light-weight apparatus cannot be satisfied.